Friday 24 Jan 2014: Heavy Metal: Lead Stars, Bling and Diffusion in Hot Subdwarfs
Dr Simon Jeffery - Armagh Observatory
Physics, 4th floor 14:00-15:00
Hot subdwarfs are hot low-mass stars which exhibit a range of surface composition and pulsation properties. They are essentially helium stars, but most have an extremely helium-poor surface. In terms of evolution, it is clear that they are formed by several different channels -- all of which are likely to produce a helium-rich surface, and most of which involve a binary companion. We will argue that a small fraction of subdwarfs with helium-rich surfaces are likely progenitors of classical helium-poor sdB stars, currently evolving onto the extended horizontal branch. As their effective temperature and surface gravity evolve, radiative levitation sorts the chemical structure of the photosphere. The result is that elements are concentrated into thin cloud layers. When one of these clouds coincides with the line-forming region in the photosphere, the spectrum of the star shows an extraordinary superabundance of exotic elements.